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497
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Why not solar thermal? I didn't realize how many options there are for converting high temperature heat and H2O/CO2 into H2/CO + O2.
http://www1.umn.edu/news/features/2011/UR_CONTENT_290042.htm...
http://eands.caltech.edu/articles/LXXII2/CO2_to_Fuel.pdf
http://addis.caltech.edu/publications/Thermochemical%20study...
http://onlinelibrary.wiley.com/doi/10.1002/aic.12580/full
http://en.wikipedia.org/wiki/Cerium%28IV%29_oxide-cerium%28I...
http://www.google.com/patents?id=EbLGAAAAEBAJ&pg=PA14&am...
It seems like there may be plentiful options for the experimenter at home in these directions. Ceria is cheap. Mirrors are not terribly tough. The
efficiency doesn't have to be that fantastic to be more attractive than a pricy PV + electrolysis system. Dealing with the high temperature materials
on the cheap could be problematic though.
I wish there was more solar thermal chemistry being done in general.
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not_important
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That's a real challenge, getting the very open form of CeO2, then heating to 1500 and quenching to 900 or lower. A bit like making NO by the
Birkeland–Eyde process, which also has recently been proposed to be driven by solar heat.
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497
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That patent forms a porous CeO2 by ball milling the raw powdered oxide with an 70%EtOH + 30%starch mixture, then pressing it into a pellet and
sintering at 1500*C. Not exactly "easy" but at least no expensive materials are required.
I didn't get the impression that rapid quenching was required in this situation. Of course the faster it cycles the more productive the process would
be.
NO from solar thermal is a great idea..
Venturi quenching with or without cooling fluid injection has been demonstrated to cool the gas quickly enough to catch >50% of the NO.
SO3 seems like another candidate for solar thermal production.
Edit:
Ehh... On further investigation this looks too inconveniently complex for anything but huge scale..
Simplicity and decentralization go well together.
It seems the obvious direction to take that is the microbial route.
Grow a native algae species in locally available wastewater.
Use the same system that delivers CO2 and removes O2 to circulate the algae and foam concentrate some algae up to maybe 3-8%. Anaerobically digest the
algae concentrate (at the same temperature as the photobioreactor) and the resulting biogas is bubbled back through the more algae to replace the CO2
fraction with O2 and remove H2S, making it a very lovely fuel... Preferably you could add a carbon rich material like sewage sludge to the digester to
improve the C:N and methane yields.
The sludge remaining after digestion is a concentrated nutrient soup that can be used for fertilizer or making more algae. In fact, anaerobic
digestion only loses about 16% of the N present. Compare that to around 50% for aerobic composting.
No it's not going to be highly efficient but 6 mil polyethylene is pretty damn cheap.. and there's not much more to it besides a means to pump some
air and water. Temperature control would be important. I just read some very interesting things regarding blown in soap foam insulation for
greenhouses. Should have very high bang/$. I think it could be applied to other situations quite beautifully. Floating the units in a solar pond might
work reasonably well too.
A little less simple, but you could also just (plasma?) reform the desulfurized biogas directly into clean syngas, which could even be scrubbed of
remaining CO2 by algae ;D
[Edited on 8-9-2011 by 497]
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497
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I don't really know where to post this.
I have been pondering a free piston linear alternator steam engine recently, trying to figure out the simplest way to construct one without a machine
shop. I had an idea that I'm surprised took me so long to realise. Why bother trying to build a piston cylinder assembly when they're already so
plentiful? Why not use a pneumatic cylinder? They may not be designed for steam, but they have basically all the other charictaristics required:
pressure ratings up to 250 psi, wear resistant/low friction seals and bearings meant for longterm continuous duty, wide variety of sizes and
dimensions, plentiful, and sooo cheap.
I searched around and found no mention of anyone trying to convert them to steam. So I'm wondering why I couldn't build a simple permanent magnet
linear alternator, hook it up to a pair of pneumatic cylinders in a push/pull arrangement and run it using a couple solenoid steam valves? The
cylinders could be easily ported to run in a uniflow arrangement if needed. The bearings/seals should be durable as there are no side loads at all. If
the original seals can't take the heat, repair kits with PTFE seals are cheap. Hell, the whole cylinder is dirt cheap if bought used.
From what I've read, I believe it is possible to construct a linear alternator that is 70-80% efficient without special tools. I don't know how high
the total system efficiency could get, but it will surely be similar or better than a traditional small steam engine, and easier to build. The fact
that Sandia was able to top 50% with a very similar engine (but using internal combustion) is a good sign. You just can't beat that level of
simplicity. If you're not a fan of vibration, you can simple oppose to identical free piston engines.
I realize that using an electric valve system is a limitation on the "rpm" but that could be surmounted by using larger/more cylinders at a slower
speed. Or maybe some kind of mechanical or magnetomechanical valve arrangement would be preferable if high power/weight ratio was required? I'm
currently contemplating a stationary unit, so cost, simplicity, and efficiency are the priority.
I was originally looking in to stirling engines for this purpose, but they simply cannot achieve that level of design and construction simplicity. And
buying a stirling seems to be not an option. The size range I'm interested in is about 1-5 kwh output for now. The heat source will be flue gas from a
gasifying biomass burner. The energy will be used to provide space heating, so I thought it was an awful waste to take all that 800*C energy and
simply bring it down to 50*C for space heating.
Am I just floating around in dream world here, or is there potential here?
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AndersHoveland
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While I strongly support renewable energy, it is mostly not practical to store electrical energy. When there is no sun or wind, reserve generators
(burning methane) will need to be used.
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bbartlog
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Quote: Originally posted by 497  | | ...Why not use a pneumatic cylinder? They may not be designed for steam, but they have basically all the other charictaristics required: pressure
ratings up to 250 psi, wear resistant/low friction seals |
I like your thinking. I suspect that the two main issues you would encounter are thermal - the seals are not designed for high temperature working
fluid - and overall wear - it's one thing to have a 'continuous duty cycle' where the cylinder operates once every two seconds, but you might be
looking at two orders of magnitude more than that.
[Edited on 4-11-2011 by bbartlog]
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watson.fawkes
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| Quote: Originally posted by 497 | | I have been pondering a free piston linear alternator steam engine recently, trying to figure out the simplest way to construct one without a machine
shop. I had an idea that I'm surprised took me so long to realise. Why bother trying to build a piston cylinder assembly when they're already so
plentiful? Why not use a pneumatic cylinder? |
Perhaps I'm missing something, but isn't what you're talking
about tantamount to a Sterling engine?
As for the construction aspects, it's a general rule that if you want to make a new kind of machine, you'll need a machine shop. In this case, you're
talking about using small-bore cylinders where you want large-bore ones. It's the line-square relationship between total displacement and sealing
surface that matters practically, not the least for reducing friction.
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497
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| Quote: | | Perhaps I'm missing something, but isn't what you're talking about tantamount to a Sterling engine? |
Not really. As far as I know you can not build a stirling engine with one moving part. Stirling engines also have problems because they have to manage
a very high hot side temperature, and high inert gas pressure is required to achieve efficiency.
If you look up schematics of free piston stirling engines, you will find they are not that simple. While possibly easier to construct than a crank
shaft style engine, it still looks much more daunting than throwing together a couple pneumatic cylinders. I suppose pneumatic cylinders could be used
for constructing a stirling engine too, but the small bore and low pressure rating is more of a limitation on the power output. As far as I know, for
a given rpm, displacement, and max pressure a steam engine will be much more powerful than a stirling. A 2' or 3' bore 6' stroke cylinder running at
150-200 psi steam pressure could actually produce useful power right? A similar sized stirling could never yield useful power as far as I understand.
Even if multiple cylinders are required, they commonly go for $20-50, so it doesn't really matter.
It wouldn't be much of a "new machine," simple double ended free piston linear alternator engines have been built before, using a variety of pressure
sources to operate them.
Some durability can be sacrificed if the engine is cheap/easy enough to construct. Seals are cheap and easy to replace. High temperature fluoropolymer
bearings and seals rated to at least 180*C are available.
[Edited on 5-11-2011 by 497]
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watson.fawkes
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I think the largest problem you're going to have it the total cycle rating on the off-the shelf solenoid valves. If they're rated, say, 1,000,000
cycles, and you're running at 100 rpm, then you're only talking about just shy of a week of continuous running. That kind of valve just isn't designed
for what you're thinking of doing with it.
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bbartlog
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| Quote: | | for a given rpm, displacement, and max pressure a steam engine will be much more powerful than a stirling. |
Now you've lost me.... don't the parameters you mention pretty well define the power output (I mean I guess you also need min pressure or better the
overall shape of the time/pressure in there somewhere but still)? Not saying that a steam engine mightn't be more powerful but if it is it would be
due to better numbers in one of those areas...
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497
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My point was just that a steam engine can developed far higher force on the piston than a stirling. To get much power from a stirling, the working gas
must be highly pressurized. Usually to many hundreds of psi. So a pneumatic cylinder is simply not very suitable.
I wondered about solenoid durability. There are so many other other options for valve gear though. I wonder about using a little variable speed
electric motor to turn a free spinning ball valve?
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Neil
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For fun, how do you kill a Stirling engine? You lubricate it.
A Stirling piston has to be designed so that it functions with essentially a frictionless seal. Air cylinders and the like have far to much friction
to ever be useful in a Stirling engine. if you build a Stirling to run off of huge thermal variations, by the time all is said and done you really
just have an inefficient steam engine.
A possibility is to use a closed steam cycle with something like ammonia so that it would function like a steam engine while still having the large
energy transfers that gives steam the kick it has.
A Stirling can generate force from very small thermal variations provided the 'working fluid' is large enough. If you put a massive expansion cylinder
on a Stirling you can run it off of the heat of your hand.
I have heard that the soviet atomic batteries used Stirling engines tied to generators but I'm not sure if that is true or not.
A purely linear engine is doomed to be inefficient for the same reason a piston engine is doomed, the energy wasted each time the piston is reversed
is significant.
Some engines where developed that tied the piston and a pump piston together in a linear format,but they used a rotating flywheel to conserve momentum
and drive the piston through the direction shifts, check out Snow engines. In the case of steam, a steam chest with a worn in slide valve is
essentially fool proof in operation and nearly indestructible.
The most efficient you can get for recovering steam energy is shoot steam at high pressure through a multistage turbine.
It would be really neat to see a purely linear steam engine in play but in terms of efficiency its not really viable...
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497
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Viable for what? Utility scale? Obviously piston anything will never be. Ever tried to build a 1kw turbine? It doesn't work. Turbines are basically
useless for small scale things. Can a small combustion turbine reach 50% efficiency? A linear alternator free piston IC can. Just saying...
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Twospoons
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Fluidyne. uses liquid "pistons" in vertical tubes.
| Quote: Originally posted by 497 |
Stirling engines also have problems because they have to manage a very high hot side temperature,
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High temp hot side is an essential part of any themal engine (assuming RT as the cold side). Sterling cycle just gets closest to the Carnot
limit.
Pneumatic cylinders are not made to handle high temps or steam. The only bits you could keep would be the outer cylinder and piston rod. All the
seals would need replacing.
Alternative 'free piston' approach is the pulse tube. Usually mechanically driven to operate as a heat pump, they can also be used as a heat engine.
Nice because the only moving parts are the working fluid, and the diaphragm at one end.
Helicopter: "helico" -> spiral, "pter" -> with wings
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497
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Ok you got me with the fluidyne. But how practical is that?
I think there is a pretty big difference between one side of the engine being exposed directly to 800 or 1000 degree flue gas versus under 200 for
steam less with other fluids...
Seals are pretty cheap. Not hard to replace either.
I guess you could put a pulse tube on either side of a free perminant magnet piston? I fear the pulse tube style operation would perform very poorly
at high temeratures. According to wikipedia pulse tube coolers have worse COPs than the alternatives unless the operating temperature is below 80K...
I assume the working fluid's density is critical to its efficiency. I wonder if the principle could be somehow adapted to operation with a condensible
working fluid? The rediculas level of simplicity is intriguing for sure.
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Twospoons
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The only use I can think of for the fluidyne is pumping water in areas where the only energy source is solar. So its not going to solve the worlds
energy crisis. Still pretty neat though - you have to admire its low tech simplicity, and the ability to use low grade heat like solar.
I've often pondered the $ per W for solar thermal electricity vs PV cells, in a small installation (say 2-3kW). Not easy to see where the break point
would be.
Helicopter: "helico" -> spiral, "pter" -> with wings
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497
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I love the simplicity of the stirling engine, particularly in a free piston arrangement. I think the main issue that needs to be solved is: how can
one build a vessel capable of withstanding 10 atm (30 would be better) while being exposed to high temperatures above 600-800*C without expensive
equipment and special skills?
That question alone is what makes me lean toward a rankine cycle system, with all its complexity and poor efficiency...
Any suggestions?
Does anyone have any ideas about a simple low tech electrically driven valve system for a rankine cycle piston engine?
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celinaaniston86
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The wind-power market is intensely backed by loan assures and requires, and like solar power is transforming out to be a wide pit of spent financing
that also increases the cost of power to areas whose resources have been necessary to buy its result. It is another ecological pipe dream and one
expected to enhance those who go into this doubtful business.
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497
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The gratzel cell is worth looking up. Cheap to build, decent efficiency.
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497
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So why the hell hasn't this been brought up before?
http://chemgroups.ucdavis.edu/~mascal/pages/biomass.html
Does it get any easier?? The levulinic acid produced by heating the chloromethylfurfural with water can be converted to high energy density liquid
hydrocarbons usable in IC engines by simply pyrolysing the calcium salt at 350-450*. Very high yields overall. Gasification of the remaining lignin
can provide excess heat, possibly to generate electricity, etc.
CMF will form the corresponding levulinic ester if heated with an alcohol, so that is another liquid fuel option, although the energy density is a bit
lower, 24MJ/kg compared to 34 for the thermally deoxygenated products.
The papers on thermal deoxygenation all talk about using Ca(OH)2 to neutralize the levulinic acid, but I don't understand why straight CaCO3 couldn't
be used...
[Edited on 20-1-2012 by 497]
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watson.fawkes
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| Quote: Originally posted by 497 | | CMF will form the corresponding levulinic ester if heated with an alcohol, so that is another liquid fuel option, although the energy density is a bit
lower, 24MJ/kg compared to 34 for the thermally deoxygenated products. |
It seems ideal for a small-scale
plant. If you first run an ethanol fermentation, the waste from that process should be usable as a feedstock for the CMF one. This could avoid all the
energy input problems with pyrolysis.
Just my first thoughts. Don't know about actual feasibility.
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GreenD
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My poiny on solar energy:
You are paying for a renewable source of energy. That is all. If you don't want to pay the extra money because something else is cheaper, the fuck are
you? What are your real intentions in life? To save money?
Same shit goes for food. You are paying for either a healthy dose of antioxidants, vitamins and minerals in expensive veggies, and even more expensive
in respectable practices of organic food, or you can buy cheap shit and poison yourself and the planet slowly.
Where is the choice in this shit? You're either a fucking idiot who does not think for his or herself and is completely molded by a society driven by
the rat race and money, or you understand what & who you are and respect the relationship of your body and the fucking rock it was born on.
My words to anyone who even wants to debate renewable energy (and off topic healthy / organic food):
go die.
PS, I believe UC Davis or Berkeley came up with a >90% photocell. It was about a millimeter^2 in area, and cost was astronomical.
I'd still purchase it.
[Edited on 20-1-2012 by GreenD]
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AndersHoveland
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It should also be remembered that some areas are much more appropriate for solar power than others. Remote desert regions, without less access to
electric lines, and with few cloudy days, would be the most appropriate locations for solar power. Ironically, the regions of the world that are the
msot enthusiastic about the environment and renewable energy are also the regions of the world with cloudy skies! If the the environmentally-minded
residents under cloudy skies want to make the best use of their money, they should pay for the more expensive solar panels in the sunnier regions, to
offset the burning of coal by residents who care less about the environment. The country of Norway, in fact, already does this to some extent in
African countries.
http://www.flyingblueclubafrica.com/business/business-for-bu...
http://www.sum.uio.no/english/research/news-and-events/event...
Also read about carbon offsets, where you can donate money for solar panels to be used in Africa, instead of installing your own solar panels if you
live in a cloudy area. For the same price, you can reduce CO2 emissions more by paying for the solar panels in Africa, where it much sunnier.
[Edited on 20-1-2012 by AndersHoveland]
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AndersHoveland
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One of the potential ways to less expensively store large quantities of electrical energy from solar panels for use on a cloudy day is the vanadium
redox battery
http://en.wikipedia.org/wiki/Vanadium_redox_battery
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White Yeti
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I think that more focus should be put into using solar energy to provide heat for industrial processes rather than generating electricity.
If you think about it, we use energy in basically two forms, electricity and heat. We need to figure out how to store heat cheaply and on a massive
scale. Molten salts could get the job done, but right now, we use molten salts to boil water and turn turbines to generate electricity instead of
heating endothermic industrial processes, like the calcination of calcium carbonate for example.
Solar alone cannot supply all the energy needed for industrial processes, but it can at least help out.
Fifth generation nuclear reactors are working towards just that; why not use solar energy for the same purpose?
According to this source, 70% of the energy industrialized countries use is in the form of heat.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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